As environmental agencies become more aware of the potential health risks associated with drinking either municipal or well water, there has been an every increasing need for residential water purification systems which are capable of removing organics, inorganics, particulate, microorganisms, bacteria and viruses from the water supply prior to consumption. Most conventional systems require a series of filtration and chlorination units to properly remove such matters from the water. These units are extremely costly to install and maintain, and take up a lot of space making them unfit for countertop use.
Filtration media has been used for years to remove particulate from the water supply, while carbon block filters have been effective in removal of organics and inorganics. However, conventional filters are incapable of removing microorganisms such as bacteria, viruses, yeasts or molds. Ultraviolet radiation in the 200-300 nanometer range have been extremely effective in killing such microorganisms. As such, germicidal lamps have been used extensively in air and water purification, sewage treatment, protection of food and beverages, and other disinfection and sterilization applications.
Water purification systems which combine the disinfection and sterilization capabilities of ultraviolet radiation with the particulate, organic and inorganic filtering capabilities of conventional filter media are known. Such combined systems provide extremely pure and sterilized drinking water regardless of the origin of the water source.
Even when such water purification systems are used, however, it has been found that bacteria remains in the water and microbial biofilms can form in pipes downstream of the system. Biofilms are formed when bacteria adheres to a hard surface in an aqueous environment. Over a period of time, microbes entering the pipe stick to the already existing bacterial layer thereby forming a microbial matrix. This matrix, once established, supplies nutrients required for growing additional microbial mass. The formation of biofilms is most pronounced in pipes formed of organic substances such as plastic and rubber, and in pipes having narrow inside diameters.
Although biofilm formation is encountered in most piping systems, the problem is particularly acute in dental unit water lines, as such water lines are usually formed of small diameter plastic tubing. Further, because the water is used in dental work, the prevention of the colonization of the dental unit water lines with bacteria is of particular importance. Nonetheless, biofilm growth has been observed inside new dental unit plastic water lines in as little as two weeks. These biofilms, when viewed through a scanning electron microscope were found to be characterized by microorganisms embedded in an amorphous matrix. The observed amorphous matrix was about 30 to 50 microns thick and capable of shedding bacteria (normal size of about 1 micron) into the water supply. Pseudomonas aeruginosa biofilm quantified by measuring distributions of thickness in biofilm samples demonstrated a mean of 33 microns (range of 13.3 microns to 60.0 microns). Most biomass tend to detach in the form of multicellular particles with some particles exceeding 100 microns in size. Large numbers of Gram-negative bacili are commonly found to be present in the water outflow/effluent of dental units. Although some organisms enter the system as occasional contaminants of the main water supply, the high counts observed are due to colonization and growth on the walls of the small bore plastic tubing of the dental unit water lines.
The most widely used method for killing microorganisms in water, and preventing the formation of biofilms, involves treating the water with chlorine. However, disinfection treatments with chlorine can produce a wide variety of byproducts, many of which have been shown to cause cancer and other toxic effects. Ozone is an extremely strong oxidant and is one of the most powerful water sanitizers readily available. Ozone deactivates bacteria and viruses 3125 times faster than chlorine.
The prior art teaches the treatment of unfiltered water with ultraviolet radiation and subsequent treatment with ozone. This prior art further teaches the use of the ultraviolet radiation source as a means for generating the ozone. Such treatments were disadvantageous, however, as without filtration, the pathogen level in the water remains high, and particulate matter, turbidity and other interfering constituents in the water reduces the efficacy of ultraviolet radiation treatment. The entrainment of ozone with water after filtration with a separate media filter, before treatment with ultraviolet light was also heretofore known. Some of these prior art units have used the ultraviolet light source to simultaneously radiate the water, and supply a source of ozone which was then entrained in the water feedstream. The injection of ozone before exposure to ultraviolet light is disadvantageous, however, as ultraviolet radiation can break down ozone, thereby decreasing the efficacy of the ozone treatment.
Two stage water purification systems as discussed above require periodic maintenance such as replacing the carbon block filter approximately every six months (more frequently if needed), replacing the ultraviolet lamp every twelve months to insure proper performance (i.e., lamp may not burn-out, but disinfection capacity does diminish over time), and cleaning of the quartz tube every six months. Although the carbon block filter is easy to replace, i.e., simply unscrew the filter housing and slide the filter off the stainless steel sleeve at the open end, replacement of the ultraviolet lamp requires substantial disassembly of the base unit of the housing. Since the ultraviolet lamp replacement is extremely difficult, many unsophisticated end-users (i.e., homeowners) will tend to simply replace the separate carbon-block filter and not replace the lamp as frequently as necessary. If the lamp is not replaced on a periodic basis its effectiveness in disinfecting and sterilizing water will diminish over time, thus posing a health risk to unwary end-users.
Therefore, it would be highly desirable to have a single unit that includes each of a media filter, an ultraviolet radiation source and an ozone treatment means, that uses the ultraviolet radiation source to simultaneously generate the ozone needed for ozone treatment. It would also be highly desirable to provide an integrated purification unit that optimally treats the water feedstream by filtering the water through a media filter, exposing the filtered water to ultraviolet radiation to kill the majority of microorganisms, and subsequently treat the filtered and radiated water with ozone to neutralize any remaining bacteria to prevent formation of biofilms and contamination in downstream waterlines. In this regard, the present inventor has developed an integrated unit that treats a water stream in the optimal manner by filtering the water through a media filter, subjecting the filtered water to ultraviolet radiation treatment, and subsequently treating the filtered and radiated water with ozone. The ultraviolet light generating source is further used to generate the needed supply of ozone, thereby reducing the complexity, cost, bulk and energy requirements of the unit. Having the carbon microfilter upstream of the ultraviolet light source offers the following advantages:
Preventing harmful cysts such as Cryptosporidium and Giardia liamblia from entering the treated water. PA1 Increasing the efficiency of the ultraviolet radiation treatment by increasing the optical clarity of the water. PA1 Removing ozone scavenging compounds from the water, thereby increasing the disinfection efficiency of the ozone. PA1 Preventing fouling of the quartz tube by preventing bio-colloids and other foulants from entering the water.
The present invention also provides many additional advantages which shall become apparent as described below.